Transmission mechanism of plant viruses transmitted by the fungus Polymyxa betae

甜菜坏死性黄脉病毒（BNYVV）是由土壤传播的真菌甜菜多粘菌传播的，含有5种ssRNA （rna 1 ~ 5）。BNYVV通过甜菜中的P. batae生物型传播，而不通过Chenopodium album、Amaranthus retroflexus和马齿苋的其他生物型传播。虽然BNYVV的寄主范围和媒介被认为仅限于Chenopdiaceae物种等少数物种，但发现P. betae游动孢子可感染广泛的植物物种，并且BNYVV还感染了其中几种植物物种的根。本拟烟是一个很好的指示宿主。外壳蛋白由RNA2的5'近端ORF编码，该ORF的末端密码子可以被抑制，从而产生75 kDa的读透（RT）蛋白。诱变分析显示，RT结构域n端一半的区域参与病毒组装，而c端蛋白质包含对真菌传播重要的序列。建立了BNYVV rna 3、4和5的感染性cDNA克隆。用含有RNA3、rna4和RNA5不同组合的分离物接种真菌试验表明，RNA3和RNA5参与了症状表达。由RNA3编码的25 kDA蛋白与甜菜感病品种的根瘤病有关，也参与了抗性品种的抗性反应。当编码26 kDA蛋白的RNA5存在时，根症状更强烈，获得抗25 kDA和26 kDA蛋白的抗血清。这表明，这些蛋白在感染植物中的表达与症状的发展密切相关。RNA4与症状表达无关，但增加了传递效率和稳定性。RNA4与RNA3或RNA5之间存在协同效应。

Beet necrotic yellow vein virus (BNYVV), which is transmitted by the soil-borne fungus Polymyxa betae, contains five ssRNA species (RNAs 1 to 5). BNYVV was transmitted by the biotype of P. batae from sugar beets, but not by the other biotypes from Chenopodium album, Amaranthus retroflexus and Portulaca oleracea. Although host ranges of BNYVV and the vector were thought to be limited to only few species such as Chenopdiaceae species, P. betae zoospores were found to infect a wide range of plant species, and also BNYVV infected roots of several plant species of them. Nicotiana benthamiana is a good indicator host. The coat protein is encoded by the 5' proximal ORF of RNA2, and the terminal codon of this ORF can be suppressed, which results in the production of a 75 kDa readthrough (RT) protein. Mutagenic analysis revealed that a region within the N-terminal half of the RT domain is involved in virus assembly, whereas the C-terminal protein contains sequences important for fungus transmission. Infectious cDNA clones to BNYVV RNAs 3,4 and 5 were established. Fungal inoculation tests with isolates containing different combinations of RNAs 3, 4 and 5 showed that RNA3 and RNA5 are involved in symptom expression. The 25 kDA protein encoded by RNA3 was responsible for rhizomania of susceptible cultivars of sugar beet, and also was involved in resistant reaction in resistant cultivars. When RNA5, encoding the 26 kDA protein, was present, the root symptoms were more intense, Antisera against 25 kDA AND 26 kDA protein, were obtained. It was suggested that expressions of these proteins in infected plant are strongly involved in symptom development. RNA4 was not associated with symptom expression, but acted as increasing transmission efficiency and stability. Synergistic effects were found between RNA4 and RNA3 or RNA5.